Journal of Structural Engineering

High-strength cold-formed steel sections are commonly used in a variety of applications including residential construction. These steel sections typically have a nominal yield stress of 550 MPa and the use of such high-strength material allows for a reduction in thicknesses. With this reduction in thickness, the high-strength steel can be manufactured into complex shapes including stiffeners. Such complex shapes exhibit structural instabilities such as local, distortional, and flexural-torsional buckling modes, and in some cases, interaction of the local and distortional buckling modes may occur. This paper describes the design and testing of web-stiffened high-strength steel cold-formed lipped channel columns. In order to be able to apply the direct strength method (DSM) in Section 7 of the Australian Standard AS/NZS 4600:2005 and Appendix 1 of the North American Specification to design, the steel sections must be prequalified as a compression member. The section chosen is prequalified and has nearly coincidental local buckling and distortional buckling loads as well as a flexural-torsional mode which varies with length. A series of compression tests was carried out in a 300-kN capacity SINTEC testing machine over a range of lengths with fixed-ended conditions. The varying lengths were chosen so as to observe the buckling modes and the possibility of interaction between them. The effect of the different types of failure modes is also discussed in this paper. The experimental results are then compared with design methods in the existing design standards. The methods include the effective width method and the DSM as described in the Australian Cold-Formed Steel Structures Standard and the North American Specification. It is shown that the existing standards are unconservative and new proposals for dealing with this are made.

Metal members are able to exhibit plastic deformations whose amplitude depends on the local slenderness of the plate elements constituting the member section, provided that global instabilities are prevented. This local slenderness depends on the width-to-thickness ratios of the plate elements and governs the occurrence of local buckling which can be developed either in elastic or in plastic range. Aiming at the development of a ductile behavior, the occurrence of local buckling in elastic range has to be prevented to assure the development of ultimate behavior in plastic range. To this scope, the width-to-thickness ratios of the plate elements constituting the member section have to be properly limited. Wide experimental research dealing with the influence of width-to-thickness ratios on the local buckling of heat-treated aluminum alloys has been recently completed with the aim of providing Eurocode 9 with the background data necessary for setting up classification criteria specific to aluminum members. The aim of the developed experimental activity is evaluation of the relationship between the strain corresponding to the complete development of local buckling and the slenderness parameters of the plate elements composing the section. This relationship has been derived by analyzing the results obtained from a great number of stub column tests carried out on specimens having width-to-thickness ratios covering the whole range of variability of commonly extruded profiles. The whole experimental program has dealt with square hollow section, rectangular hollow section members, channels, and angles made of 6,000 series alloy, provided by the major European aluminum industries. This paper presents and discusses the results of the part of the experimental program regarding aluminum alloy angles subjected to local buckling under uniform compression. Sixty-four stub column tests have been carried out at the Material and Structure Laboratory of the Department of Civil Engineering of Salerno University. These experimental results and their interpretation are presented in this paper. In addition, a classification criterion accounting for the interaction between the two slenderness parameters of the cross-section is proposed.

A simple constitutive model for the inelastic response of steel under monotonic and random cyclic loading conditions is developed within the framework of bounding surface plasticity. The particular feature that distinguishes this model from other similar ones is the ability of the bounding surface formulation to describe in a very simple way the initial “plateau” type of perfectly plastic response that many kinds of structural steels exhibit upon initial yield in tension or compression, before hardening begins. The key constitutive element is to assume a fixed nonhardening bounding surface during the plateau response until a cumulative plastic strain threshold is reached, while the yield surface softens isotropically and hardens kinematically. In this way not only monotonic but also cyclic loading within the plateau range can be easily described. Three kinematic hardening rules for the bounding surface are explored. The development is focused on uniaxial loading conditions that are typical in many structural engineering applications employing a fiber-based discretization of the cross section. Several simulations to demonstrate the effectiveness of the proposed model are presented. Finally, its extension to a multiaxial stress generalization is concisely presented for future use.

A rate-independent cyclic plasticity model for structural steels with a yield plateau is proposed. The model couples nonlinear kinematic hardening with a memory surface in the plastic strain space, to account for the progressive cyclic hardening/softening effects and a pseudomemory surface in the deviatoric stress space to correctly describe the plateau response. A simple identification procedure to calibrate the material dependent parameters is outlined and the accuracy of the proposed model is verified against experimental data available in the literature for proportional and nonproportional loading paths.

The dynamic analysis of inelastic structures with geometric nonlinearities experiencing large deformations and buckling is challenging, in particular, if three-dimensional space effects are considered. This paper introduces a new formulation of a three-dimensional beam-column element and the associated analysis of the global frame system using a corotational approach formulated in the state space. The corotational approach may allow uncoupling of the local large deformations and inelastic buckling of the element from the large deformation of the global system. Shaking table testing performed by the authors on a steel frame model structure provides benchmark information for comparison with the proposed analytical formulation.

For convenience, a horizontally circular curved beam without any attachments is called a “bare” curved beam and the one carrying any attachments is called a “loaded” curved beam, in this paper. For the out-of-plane free vibrations of bare curved beams, one can find some exact solutions from the existing literature, but this is not true for those of the loaded curved beams. One of the main reasons for the last situation is due to the difficulty of solving a complex-variable eigenvalue equation. It is well known that the half-interval method is one of the simplest techniques for searching the roots of an eigenvalue equation. However, it suffers difficulty if the eigenvalue equation is a determinant form $\left(\left|H\left(\omega \right)\right|=0\right)$ with some (or all) of its coefficients $\left[H_{i,j}\left(\omega \right)\right]$ being the complex numbers, because it is difficult to find a trial root $\left({\omega }^t\right)$ so that both the real part $H_R$ and imaginary part $H_I$ of the associated determinant value $\left|H\left({\omega }^t\right)\right|$ are equal to zero simultaneously (i.e., $H_R=H_I=0$ ). Furthermore, the magnitude of the determinant value is greater than or equal to zero (i.e., $\overline{H}=\sqrt{H_R^2+H_R^2}\ge 0$ ). To overcome the last difficulty, this paper presents a technique to replace all complex coefficients of the eigenvalue equation by the real ones, so that the conventional half-interval method may be easily applied to determining the “exact” solution for the natural frequencies and mode shapes of out-of-plane free vibrations of a uniform curved Euler-Bernoulli beam carrying arbitrary sets of concentrated elements in various boundary conditions, where each set of concentrated elements includes a lumped mass, a linear spring, a bending spring and a twisting (torsional) spring. To confirm the reliability of the presented theory and the developed computer program, most of the exact solutions for natural frequencies and mode shapes obtained from the presented approach are compared with the “approximate” ones obtained from the conventional finite-element method and good agreements are achieved.

Detuning, resulting from deterioration, inadvertent changes to structure properties, and design forecasting, can lead to a significant loss of performance in tuned mass dampers (TMDs). To overcome this issue, an adaptive compensation mechanism for suspended pendulum TMDs is proposed. The adaptive pendulum mass damper is a three-dimensional pendulum, augmented with a tuning frame to adjust its natural frequency, and two adjustable air dampers adjust damping. The adjustments for the natural frequency and damping compensation are achieved using a system of stepper motors and a microcontroller. There are two major components in the proposed methodology: identification and control, one followed by the other, in that order. The identification is carried out using spectral information obtained from the structural acceleration responses. The performance of the adaptive pendulum system is studied via both experiments and simulations. The main contribution of this paper is to develop an effective means of compensation for detuning in TMDs, while retaining the simplicity of passive pendulum TMDs. The proposed methodology allows pendulum TMDs to be tuned in place using relatively simple hardware and algorithms, based on ambient vibration measurements only.

This paper presents analytical assessment of the effect of vertical earthquake ground motion on RC bridge piers. A bridge structure damaged during the Northridge Earthquake and a Federal Highway concept bridge design are examined. The effects of a suite of earthquake ground motion records with different vertical-to-horizontal peak acceleration ratios on the two bridges are presented and the results are compared with the case of horizontal-only excitation. The effects of arrival time interval between horizontal and vertical acceleration peaks are also reported and compared to the case of coincident motion. It is observed that the inclusion of the vertical component of ground motion has an important effect on the response at all levels and components. It is therefore concluded that vertical motion should be included in analysis for assessment and design, especially that there are no particular challenges impeding its inclusion.

This paper reports the experimental results of symmetrical push-out tests performed on notched and toothed metal plate connectors for laminated veneer lumber (LVL)-concrete composite floor systems. The characteristic shear strength and slip moduli were evaluated for three types of connectors: (1) a 300-mm-long rectangular notch cut in the LVL joist and reinforced with a 16-mm-diameter lag screw; (2) a triangular notch reinforced with the same lag screw; and (3) two 333-mm-long toothed metal plates pressed in the lateral surface of two adjacent LVL joists. The shear force versus relative slip relationships are presented together with analytical prepeak and postpeak approximations which can be used to carry out nonlinear finite-element analyses of LVL-concrete composite beams. The failure mechanisms of the notched connections are also discussed. Analytical design formulas for shear-strength evaluation of notched connections derived in accordance with New Zealand Standards and Eurocodes are proposed based on four possible failure mechanisms. Good approximation was found if a slight modification of the Eurocodes formulas is introduced.

Equations to obtain equivalent rectangular stress-block parameters for unconfined and confined concrete are derived for rapid (hand) analysis and design purposes. To overcome a shortcoming of existing commonly used stress-strain models that are not easy to integrate, a new stress-strain model is proposed and validated for a wide range of concrete strengths and confining stresses. The efficacy of the equivalent rectangular stress-block parameters is demonstrated for hand calculations in predicting key moment-curvature results for a confined concrete column. Results are compared with those obtained from a computational fiber-element analysis using the proposed stress-strain model and another widely used existing model; good agreement between the two is observed.